After-develop inspection (ADI) and photo-cell monitoring (PM) are part of a comprehensive lithography process
monitoring strategy. Capturing defects of interest (DOI) in the lithography cell rather than at later process steps shortens
the cycle time and allows for wafer re-work, reducing overall cost and improving yield. Low contrast DOI and multiple
noise sources make litho inspection challenging. Broadband brightfield inspectors provide the highest sensitivity to litho
DOI and are traditionally used for ADI and PM. However, a darkfield imaging inspector has shown sufficient sensitivity
to litho DOI, providing a high-throughput option for litho defect monitoring. On the darkfield imaging inspector, a very
high sensitivity inspection is used in conjunction with advanced defect binning to detect pattern issues and other DOI
and minimize nuisance defects. For ADI, this darkfield inspection methodology enables the separation and tracking of
'color variation' defects that correlate directly to CD variations allowing a high-sampling monitor for focus excursions,
thereby reducing scanner re-qualification time. For PM, the darkfield imaging inspector provides sensitivity to critical
immersion litho defects at a lower cost-of-ownership. This paper describes litho monitoring methodologies developed
and implemented for flash devices for 65nm production and 45nm development using the darkfield imaging inspector.

Process Window Qualification (PWQ) is a well-established wafer inspection technique used to qualify the design of
mask sets and to characterize lithography process windows. While PWQ typically employs a broadband brightfield
inspector, novel techniques for patterned wafer darkfield inspection have proven to provide sufficient sensitivity along
with noise suppression benefits for lithography layers. This paper describes the introduction and implementation of
PWQ on patterned wafer darkfield inspectors. An initial project characterized critical PWQ requirements on the
darkfield inspector. The results showed that this new approach meets performance requirements, such as defect of
interest (DOI) detection and process window characterization, as well as ease-of-use requirements such as automated
setup for advanced design rule products.

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Journal of Applied Remote SensingJournal of Astronomical Telescopes Instruments and SystemsJournal of Biomedical OpticsJournal of Electronic ImagingJournal of Medical ImagingJournal of Micro/Nanolithography, MEMS, and MOEMSJournal of NanophotonicsJournal of Photonics for EnergyNeurophotonicsOptical EngineeringSPIE Reviews